Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $67.65   8.501%   $73.4009   $73.40   $73.40   $73.40  
  Purchase #2 $90.71   3.476%   $93.8631   $93.86   $93.85   $93.90  
  Purchase #3 $230.68   6.436%   $245.5266   $245.53   $245.55   $245.50  
  Purchase #4 $192.70   9.750%   $211.4883   $211.49   $211.50   $211.50  
  Purchase #5 $68.41   11.489%   $76.2696   $76.27   $76.25   $76.30  
  Purchase #6 $62.74   10.782%   $69.5046   $69.50   $69.50   $69.50  
  Purchase #7 $49.96   13.481%   $56.6951   $56.70   $56.70   $56.70  
  7 purchase totals = $762.85       $826.7482   $826.75   $826.75   $826.80